1. Field of the Invention
This invention relates to a method for extending the shelf-life of human blood platelets. The invention relates particularly to a reversible inhibitor system and method that inhibits platelets from biologically activating during storage at refrigeration temperatures (4.degree. C.) but leaves platelets with the ability to resume normal reactions once the inhibitor system is removed.
2. Description of Related Art
Platelet transfusions are frequently used to treat patients. Not only are platelet transfusions given to casualty victims suffering from massive blood loss, but also to patients undergoing chemotherapy. Chemotherapy reduces the number of a patient's platelets, and also causes the platelets that are present to function defectively. For example, with thrombocytopenia, a patient has a decreased number of platelets caused by bone marrow suppression, whereas a patient with hemorrhagic myocarditis may have platelets that have been rendered functionally defective by chemotherapy. Platelet transfusions are used to increase the number of platelets to treat conditions such as thrombocytopenia, and to replace functionally defective platelets in treating hemorrhagic myocarditis.
Blood platelets should be stored at the lowest temperature possible to reduce metabolic function, contaminant growth and the generation of cytokines. Currently, platelets are stored for up to 5 days at 22.degree. C. This storage time is limited by a decrease in pH due to increased lactate associated with anaerobic metabolic activity. Storage at 22.degree. C. is also limited by the potential for bacterial growth. Refrigeration offers advantages over 22.degree. C. storage with respect to metabolic function, contamination, and pH stability. However refrigerated storage results in multiple inherent problems. First, platelets undergo a change from discoid shape to a spherical configuration after about 24 hours of refrigerated storage. Second, spontaneous aggregation is increased after 24-48 hours of refrigerated storage. Third, platelets stored at 4.degree. C. fail to recover functional activity following the storage period. Finally, platelets which undergo a storage lesion at 4.degree. C. are cleared from the circulation by the spleen following transfusion.
Goals for refrigerated platelet storage are to preserve a high number of platelets, lengthen the time that platelets may be preserved, maintain the functional integrity of platelets, inhibit the production of cytokines in the platelet preparation, and ensure that their in vivo circulatory life span approaches normal limits. This may be accomplished by using the inhibitor system of this invention, because it blocks pathways that are essential to activation, thus rendering the platelet unsusceptible to 4.degree. C. induced damage.
Since fresh platelets have a shelf-life of only 3 to 5 days at 22.degree. C. (room temperature), methods for extending platelet shelf-life would be beneficial. Unfortunately, despite a number of attempts to optimize platelet storage, progressive changes in cell shape (resulting in biological disfunction) and permanent deterioration in subsequent aggregation potential continue to limit platelet storage. Cytokines generated during the storage of platelet concentrates can cause febrile reactions in recipient patients. In addition, platelets develop a lesion with storage that causes them to be removed from the circulation, predominantly by the spleen during the first passage following transfusion. In addition, For instance, the typical life span of a normal platelet in the human body is approximately eight days. Prior art attempts to store platelets for extended periods of time result in the creation of lesion-modified platelets. Approximately 80%-90% of the prior art storage platelets can be numerically recovered after storage, but only 20%-35% remain active after the first circulatory flow through the spleen. This is because the spleen filters out the lesion-modified platelets. Use of the compositions and methods of this invention result in the same 80%-90% numerically recovered as the prior art, but since lesion-modified platelets are not produced, 65% to 80% of the reactivated platelets should function biologically for the typical time in the human body.
Several approaches such as reduced storage temperature, cryopreservation techniques, additives and artificial storage media yield an increased number of platelets following storage. However, the functional capacity and persistence in circulation of the platelets recovered by these methods is limited. Blood banks and hospitals very much need a platelet storage system that provides an increased number of platelets after storage, but also prevents platelets from aggregating during storage and enables them to continue to retain the ability to react normally once they are transfused into a patient including the ability of platelets to persist in the circulation and not be cleared.
Blood banks and hospitals very much need a platelet storage system that will provide an increased number of platelets after storage. This may be accomplished by a platelet storage system that: prevents platelets from aggregating during storage; prevents the production of a febrile reaction in patients produced by cytokines; enables platelets to regain the ability to react normally after removal from storage; and allows platelets to persist in circulation and avoid being cleared by the spleen.
Previous attempts to use platelet activation inhibitors have met with very limited success. This is primarily because the prior art teaching is limited to the use of a single inhibitor in an attempt to preserve platelet function. The single inhibitor system results in improved results over no inhibitor at all but does not approach the unexpected results achieved using the compositions and methods of the subject invention. Prior methods for the use of single inhibitor systems are explained in Valeri, Feingold, and Marchionni, A Simple Method for Freezing Human Platelets Using Dimethylsulfoxide and Storage at -80.degree. C., Blood, Vol. 43, No. 1 (January), 1974 and Bode, Holme, Heaton, and Swanson, Extended Storage of Platelets in an Artificial Medium with the Platelet Activation Inhibitors Prostaglandin E, and Theophylline, Vox Sang 1991:60;105-112.
The instant invention represents a quantum leap in beneficial result and technical sophistication over the prior methods. The platelet storage, reactivation, and long term functional effectiveness of blood platelets treated with the compositions and methods of this invention have previously been considered impossible.